1x MythicPlusDrop/module/Schedule.lua:167: attempt to index local 'affix' (a nil value)
[string "@MythicPlusDrop/module/Schedule.lua"]:167: in function <MythicPlusDrop/module/Schedule.lua:134>
[string "=[C]"]: in function `Update'
[string "@Blizzard_ChallengesUI/Blizzard_ChallengesUI.lua"]:116: in function <...dOns/Blizzard_ChallengesUI/Blizzard_ChallengesUI.lua:107>

Locals:
weeklyChest = Frame {
Highlight = Texture {
}

I have no gametime at this moment, can you test this version pls:
MythicPlusDrop.zip

Here is a other version for testing:
MythicPlusDrop.zip

I tried both and for now no lua error appears.
Neither does the debug line you added

Ok I'll upload the version to curseforge tomorrow, but without debug output. Thx for testing the files.